1. Field of the Invention
The present invention relates generally to an apparatus allowing for simultaneous drilling and casing of a subterranean well. In a further aspect, the invention relates to a rotatable drill shoe coupled with a section of casing and a method of drilling and completing a subterranean well using the same.
2. Description of the Prior Art
Conventional techniques of constructing oil and gas wells, especially deep sea wells, involve drilling a well bore using a string of drill pipe having a drill bit attached to the lower end thereof. As the drill string is advanced into the ground, it encounters different rock formations, some of which may be unstable. In order to minimize problems which may arise in connection with traversing these various formations, the drill bit is run to a desired depth and then the drill string is removed from the well bore. Next, casing is lowered into the well bore and cemented in place. Essentially, the casing acts as a lining within the well bore and prevents collapse of the well bore or loss of drilling fluids into the formations.
This conventional technique requires two separate trips in and out of the well bore in order to complete the well, ignoring any subsequent trips for increasing the depth of the well bore which may be required. Each trip into and out of the well bore can require hours or even days depending upon the depths involved and leads to costly nonproductive time. Combining these two trips into one would significantly reduce the time involved in well completion and costs associated therewith.
Attempts have been made to drill while running casing. These attempts have generally involved using a drill bit rigidly secured to the casing and then rotating the entire casing string in order to turn the drill bit. There are a number of problems associated with this method, especially in the context of deep sea drilling. In deep sea drilling, the casing has a subsea wellhead installed at the top thereof. Conventional drill string is run through the well head and is carried by the drilling rig. The rotation of the casing in the open water between the drilling rig and the mud line can create large stresses at the interface between the casing and the drill pipe. The rotation of the large casing used in deep sea wells in a relatively high water current may also cause vibrations or high excursions from the well center. Furthermore, when landing casing with a high pressure subsea wellhead installed into a low pressure wellhead, rotation may damage one or both wellheads.